Deep bed thickener/clarifiers with enhanced liquid removal

ABSTRACT

The enhanced deliquifying of the compacted bed of deep bed thickener/clarifier is disclosed. Such an apparatus comprises a vessel receiving a slurry of liquid and solid particles suspended in the liquid. The vessel defines a free settling zone, a hindered settling zone intermediate, an upper clarification zone and a lower compaction zone. A deliquifying member is provided in the vessel extending up between at least two zones for facilitating the upward flow of free liquid from one of the lower zones and the settling of particulates. A rotating rake shaft with pickets are so designed to release the interstitial liquid trapped in a lower zone. The pickets provide pathways for liquid to release generally vertically. The release liquid travels upward to the deliquifying member and on into the clarification zone. The lower zone, freed of the interstitial water, further collapses becoming more concentrated or dense.

This application claims the benefit of provisional application Ser. No.60/147,652 filed Aug. 6, 1999.

BACKGROUND OF THE INVENTION

This invention relates to clarifiers and thickeners of the deep bedtype. This invention also relates to an associated method for separatingliquid and solid particles in a suspension of slurry in thickness andclarifiers.

Deep bed thickeners and clarifiers (or so-called thickener/clarifierdevices) are shown and described, for example, in U.S. Pat. Nos.5,433,862, 5,549,827 and 5,800,715, the disclosures of which are herebyincorporated by reference herein.

The device described in U.S. Pat. No. 5,433,862 comprises a vesselreceiving a slurry of liquid and solid particles suspended on theliquid. The vessel defines a hindered settling zone in which the liquidand solids of the slurry tend to separate with the solids settling downinto a compaction zone below the hindered settling zone. In thecompaction zone, the solids concentration tends to increase, while theliquid phase rises to a clarification zone above the hindered settlingzone. An overflow launder adjacent the upper end of the vessel receivesthe overflow phase of the slurry separated in the vessel. An underflowdischarge port toward the bottom of the vessel receives the thickened orunderflow phase of the slurry separated in the vessel. One or moreso-called separating members are provided in the vessel extendingupwardly from a lower end in the hindered settling or compaction zonesto an upper end in a clarification zone. Preferably, this memberincludes cones or other downwardly inclined surfaces that facilitateboth the settling of solids down to the compaction zone and the upwardflow of free liquid from the hindered settling and/or compaction zone tothe clarification zone.

The deep bed thickener or clarifier device described in U.S. Pat. No.5,800,715 is similar to that disclosed in U.S. Pat. No. 5,433,862, butfurther has a fluid flow barrier between the overflow clarification zoneand the other zones of the vessel, and one or more clarifying conduitsextending through the barrier. Each such conduit carries a suspendedfloc bed of particulate solids that filters and further clarifies theliquid flowing up from the hindered settling zone to the clarificationzone. This further filtering removes solid particles that wouldotherwise be carried along the “clarified” liquid to the overflowlaunder. These clarification conduits thus serve a significantlydifferent purpose than do the separating members and functionindependently thereof.

Deep bed thickener/clarifiers offer certain design and operationaladvantages over the conventional thickeners and clarifiers whileproviding clarity of overflow and solids concentration of underflowcomparable to that of conventional thickener/clarifiers. Such thickenersand clarifiers are typically of low-profile design (i.e., shorter inheight but of much greater diameter than deep bed thickeners), but likedeep bed thickeners have generally central feedwells and underflowunderflow discharge ports.

Conventional low profile thickeners rely on the radial expanse of thehorizontal settling zones to effect settling of the slurry throughoutthe thickener. To achieve this settling action, the influent feed istypically dispersed radially outwardly from the central feedwell androtating rake arms, having generally plow shaped blades, gather andlaterally direct the settled solids along the thickener/clarifier bottomto the central discharge opening in the bottom of thethickener/clarifier tank. These rake blades are located closely adjacentthe tank bottom and are designed to move the solids across the tankbottom with minimal disruption in the downward (or settling) flowpattern of the slurry though the hindered settling and compaction zones.Consistent with this purpose, the rakes are rotated at a very slow speedfor example, less than 1 revolution per minute. U.S. Pat. Nos.4,082,671, 4,217,916 and 4,271,027, for example, describe and illsutraterake assemblies that perform this function of moving settled solidsacross the tank bottom of conventional low-profile thickeners fordischarge at a central underflow outlet. Indeed, some of the rakeassemblies are intended to scrape the settled solids from the tankbottom, see U.S. Pat. No. 4,247,400.

In contrast, “deep bed” thickener/clarifiers rely on the height of thehindered settling to cause separation of the slurry into its clarifiedliquid and settled solids phases. Deep bed thickeners/clarifiers furtherhave a deep, high angle conical bottom for directing the settled solidstoward the discharge opening. Thus there is no need for rotating rakesto move the solids within the thickener/clarifier to effect removal ofthe solids. Indeed, rakes would serve little purpose in moving thesolid, but rather would add expense and operating complexity.

Basically, deep bed thickeners rely on a conical tank bottom having asidewall extending an angle from horizontal generally greater than theangle of repose of the settled solids to direct the solids to move bygravity alone along the tank bottom to the discharge opening. Thiseliminates the need for a rotating rake and thereby simplifies theoperation and construction of the thickener/clarifier as well as reducesthe cost of the thickener/clarifier compared to conventionalthickeners/clarifiers. This cost reduction takes the form of theelimination of a capital expenditure for the rake assemblies, as well asthe elimination of the associated torque driveheads and motors (often inexcess of 1,000,000 foot pounds torque) and high strength bridgesspanning the tank top to support the drive.

In contrast, conventional low profile thickener/clarifiers have tankbottoms that are flat or inclined at angles generally below the angle ofrepose of the settled solids and thus require rake assemblies and theassociated drive and bridge (or column) structures to remove the settledsolids from the thickener/clarifier.

SUMMARY OF THE INVENTION

The present invention enhances liquid-solids separation in a deep bedthickener/clarifier and thus produces an underflow product or sludgewhich is thickened relative to that of existing deep bedthickeners/clarifiers.

More particularly, the deep bed thickener/clarifier of this inventionprovides for the release and removal of free or interstitial liquid(typically water) trapped in the settled solids in the hindered settlingzone and/or the compaction zone. This release of liquid is effectedwithout increasing the size of the thickener/clarifier, disturbing thesettling processes or the naturally occurring movement of the solidsalong the conical tank bottom.

The deep bed thickener/clarifier of the present invention comprises avessel with an overflow launder and an underflow discharge port. Thevessel has an inlet for receiving a slurry of a liquid and solidparticles suspended in the liquid. In an upper portion of the vessel, afree settling zone has a low concentration of solid slurry particles,while in a lower portion of the vessel, a compaction zone has a highconcentration of solid slurry particles. The overflow launder isattached to the vessel adjacent an upper end thereof for discharge of anoverflow phase of the slurry that has been separated in the vessel. Theunderflow discharge port is adjacent to a bottom thereof for dischargeof a thickened, underlow phase of the slurry that has been separated inthe vessel.

An upper portion of the vessel holds the free settling zone and a lowerportion of the vessel holds the compaction zone. A hindered settlingzone extends between the free settling and compaction zones, with thehindered settling zone and compaction zone constituting lower settlingzones. A deliquifying member is positioned in the vessel extending upfrom adjacent the lower portion of the vessel to adjacent the upperportion of the vessel for flow of liquid from at least one of the lowerzones to the free settling zone. The deliquifying member further servesto isolate this flow of liquid from the flow of slurry down in the lowersettling zones. A rake assembly is mounted for rotation in the lowerportion of the vessel, with the rake assembly forming channels in theslurry held in the lower portion of the vessel for releasing liquid inat least one of said lower settling zones to flow to the deliquifyingmember and on to the free settling zone.

The method of this invention for operating a deep bedthickener/clarifier comprises, in accordance with the present inventionfeeding, into a vessel, a slurry of a liquid and solid particlessuspended in the liquid and separating the slurry by gravity intodifferent zones having respective degrees of liquid-solids separationincluding, at an upper portion of the vessel, a free settling zonehaving a low concentration of solid slurry particles and furtherincluding, at a lower portion of the vessel, a compaction zone having ahigh concentration of solid slurry particles. A hindered settling zoneis positioned between these zones. The method also comprisesdischarging, into an overflow launder attached to the vessel proximatelyto an upper end thereof, an overflow phase of the slurry that has beenseparated in the clarification zone and discharging, via an underflowdischarge port fixed to the vessel at least proximately to a bottomthereof, a thickened, underflow phase of the slurry that has beenseparated in the vessel. Liquid is directed from at least one of thelower settling zones to the free settling zone via a flow path which isisolated from the flow of slurry down in the vessel in the lowersettling zones. In accordance with his invention, upwardly, extendingchannels are formed in the slurry held in the lower portion of thevessel to release liquid in at least one of the lower settling zones toflow to the isolated flow path and then to the free settling zone.

Other objects of the invention will be in part apparent and in partdescribed and shown in the following description of the drawings andpreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present invention, reference should bemade to the following detailed description of the preferred embodiments,taken in conjunction with the accompanying drawings, in which likeelements have been given like numerals and wherein:

FIG. 1 illustrates a vertical section of the thickener/clarifier of thisinvention and its various components including the deliquifying memberand a rake assembly;

FIG. 2 illustrates a vertical section of a second thickener/clarifier ofthis invention with the rake shaft passing through the inside of thedeliquifying member; and

FIG. 3 illustrates the enlarged detail of a rake picket in the slurryfor forming a water flow channel in the slurry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 1, a deep bed thickener/clarifier of thisinvention, generally indicated at 10, comprises a vessel 11 having aninlet 12 receiving a slurry comprising liquid and solid particlessuspended in the liquid. The slurry components are separated in vessel11 into a relatively light-weight overflow phase (i.e., a primarilyclarified liquid) and a relatively heavy underflow phase (i.e., aprimarily high solid concentration). Vessel 11 includes a downwardlytapering frusto-conical bottom 14 having an apex (not designated)connected to an underflow discharge port 16 for the discharge of thethickened, underflow phase of the slurry that has been separated invessel 11. A variable speed pump and motor 18 communicate via a valve 65with discharge port 16 for the controlled removal of the underflow fromvessel 11. Alternatively, a remotely actuated valve (not shown) may beprovided as a mechanical end use device at discharge port 16 to controlthe removal of the underflow.

The thickener/clarifier 10 further includes an overflow weir or launder20 for removal of the overflow phase separated from the slurry in vessel11. An upper lip (not designated) of launder 20 defines the upper levelof the clarified liquid. A cylindrical wall 26 in vessel 11 forms anannular chamber 27 and defines a fluid barrier between the annularchamber and the remainder of the vessel interior. Projecting through alower wall or panel 28 of annular chamber 27 is one or more elongateconduits 30 having generally vertically extending sidewalls whichsupport fluidized floc beds 32 of the particulate material suspended inthe different conduits, as described in greater detail in U.S. Pat. No.5,800,715. Two such conduits 30 are shown in FIG. 1. However, othervessel designs may have only one such conduit or more than two conduits.Conduits 30 are shown to be of square or circular shape in section, butmay be of any shape in section.

To facilitate flocculation in vessel 11, a settling agent such as apolyelectrolyte may be delivered as an additive to the slurry or asshown in FIG. 1 preferably to the free settling liquid in the vessel. Asshown in FIG. 1. a source of settling agent such as a storage tank 36 isin fluid flow communication with the vessel 11. A fluid flow controldevice, such as a remotely actuated valve 40, regulates the dosage ofsettling aid delivered to the slurry and thus control the extent of flocformation within vessel 11.

The slurry received and held in vessel 11 separates by gravity into ahindered settling zone 42 which is located above a compaction zone 44and below an interior free settling clarification zone 46 and anoverflow clarification zone 47 in annular chamber 27. Within hinderedsettling zone 42, the liquid and solid particles tend to separate withthe solid particles tending to flow downwardly to the compaction zone 44and with the clarified liquid flowing up to clarification zone 47.Within compaction zone 44 the solids concentration increases to thehighest level of concentration at discharge port or outlet 16 at thevessel bottom.

As described in U.S. Pat. No. 5,433,862, a deliquifying member 48extends up within vessel 11 from generally adjacent the compaction zone44. Deliquifying member 48 is of generally tubular configuration andreceives free liquid released from compaction zone 44 and delivers theliquid to the upper end of the deliquifying member 48 which ispreferably positioned at the interior free settling clarification zone46. At its upper end, deliquifying member 48 is provided with openings52 for feeding expressed liquid to the free settling clarification zone46. In the thickener/clarifier of FIG. 1, the deliquifying member 48also serves as part of a rotary drive member or rake shaft as describedmore fully hereinafter.

The vessel comprises an upper portion, indicated generally at 81,holding at least a portion of the free settling zone 46 and a lowerportion, indicated generally at 83, holding at least a portion of thecompaction zone 44. The hindered settling zone 42 may extend into eitherthe upper or lower portion of the vessel. The compaction zone 44 andhindered settling zone 42 constitute lower settling zones. Thedeliquifying member 48 in the vessel extends up from the lower portion83 of the vessel to the upper portion 81 of the vessel for flow ofliquid from at least one of the lower settling zones to the freesettling zone while isolating the flow of liquid from the flow of slurrydown into the lower settling zone. A rake assembly 63 is mounted forrotation as indicated at 60 in the lower portion 83 of the vessel andhas a plurality of generally vertical pickets 62. As shown in FIG. 3, asthe rake assembly rotates the pickets 62 travel through the slurry, seearrow 80, and form temporary channels 76 in the slurry held in the lowerportion of the vessel. These channels release free or interstitialliquid in pockets 75 in at least one of the lower settling zones to flowalong generally vertical paths 72 to the deliquifying member 48. Fromthere, the liquid is free to flow on to the free settling zone 46. Thedeliquifying member 48 supports and rotates the rake assembly 63. At itsupper end, deliquifying member 48 is operatively connected to a motor 70via a drivehead 61. The motor 70 may be of fixed or variable speed, anduse any suitable motive power, such as an electric or hydraulic motor ora combustion engine.

Accordingly, the deliquifying member 48 facilitates removal of freeliquid from at least one of the lower zones to enable solids in thecompaction zone to increase to a higher concentration level and to do somore rapidly than would otherwise be possible. The deliquifying member48 is open to hindered settling zone 42 to facilitate release of freeliquid from that zone. To that end. deliquifying member 48 is providedwith one or more suitable inclined members such as upwardly taperingconical deliquifying baffles 56 shown, for example, in FIG. 1 as beingganged in a sequence. Each conical deliquifying baffle 56 is open at alower end 50 and guides released liquid upwardly along an inner surface(not shown) to a respective opening or aperture 54 provided indeliquifying member 48. Settling solids particles are directed along theouter surfaces of conical deliquifying baffles 56 towards the bottom ofvessel 11. Thus the deliquifying member 48 isolates the upward flow ofliquid from the downward flow of the slurry.

Deliquifying member 48 provides a conduit for the flow of free liquidthus released from hindered settling zone 42 and compaction zone 44.This channeling of the released liquid in those zones influences thesolids settling rate therein. Deliquifying member 48 is shown to be atube of circular or square cross-section. However, deliquifying member48 may be of other shapes as described and shown in U.S. Pat. No.5,433,862. The word “tubular” is used herein to mean a hollow profile ofany suitable cross-sectional shape.

In operation, deliquifying member 48 is rotated at a slow rate duringthe gravity settling process. The consequent movement of the pickets 62through the thickened slurry or sludge in the lower zones releasesotherwise trapped interstitial liquid 71. This freed liquid 71 generallyescapes from compaction zone 44 in laminar flow paths along pickets 62,as illustrated in FIG. 3. The overall process of thickening orclarification in apparatus 10 is controlled by adjusting the underflowwithdrawal and overflow discharge rates relative to the inlet.Thickener/clarifier 10 as provided with a rotatable rake assembly 63provides for higher underflow solids concentration, improved overflowclarity, increased rate of influent feed, reduced settling aid usage orany combination of these advantages or results than would be possible intreating slurries in conventional deep bed or low-profile, largediameter thickener/clarifiers.

Thickener/clarifier 10 includes a cover plate or upper panel 74 whichcarries drivehead 61 and motor 70. An outlet port 75 is provided at theupper end of vessel 11 for discharging the clarified liquid phase whichspills over weir or launder 20. The deliquifying member 48 is rotatablysuspended from cover plate or upper panel 74.

FIG. 2 depicts a second embodiment of the thickener/clarifier 110 Whichincludes certain modifications with respect to the apparatus of FIG. 1.Like structures in FIGS. 1 and 2 are designated with the same referencenumerals.

In FIG. 2, the deliquifying member 148, unlike the deliquifying member48 in FIG. 1, does not serve to rotate the rake assembly and may berigidly fixed to cover or upper panel 74. The deliquifying member 148 isalso shown to terminate at an upper end of a lowermost conicaldeliquifying baffle 56.

Thickener/clarifier 110 includes a rotatable rake 163 having a pluralityof generally parallel vertically extending pickets 162. Rake 163 servesto augment or accelerate the deliquifying of the lower zones. Rake 163is rotated by a drive shaft 166 which is generally coaxially andlongitudinally disposed in deliquifying member 148. Drive shaft 166 isrotatably journaled in cover plate or upper panel 74 and is operativelyconnected to drivehead 61 and motor 70.

The upper three conical deliquifying baffles 56 communicate with a lumenor interior (not designated) of fluid flow member 148 via openings orapertures 154 provided in tubular fluid flow member 148. As discussedabove, settling solids particles are directed along the outer surfacesof conical deliquifying baffles 56 towards the bottom of vessel 11.

The embodiment of FIG. 2 also differs from that of FIG. 1 in notincorporating clarification tubes (such as tubes 30) and in directingflocculant to the free settling zone at the exterior of the deliquifiingmember 148.

Although the invention has been described in terms of its preferredembodiments, those skilled in the an will recognize that numerousmodifications and changes may be made while remaining within the scopeand spirit of the invention. For example, pickets 62 and 162 of rakes 63and 163, respectively extend parallel to one another vertically throughcompaction zone 44 and into hindered settling zone 42. Pickets 62 and162 may be attentively inclined at an angle to the vertical. Inaddition, conical deliquifying baffles 56 may be greater or fever innumber than four. The conical deliquifying baffles located below chamber27 may be larger. In addition, the pickets may be positioned and be ofsufficient length to extend into both the compaction zone 44 andhindered settling zone 42. The deliquifying member 48, 148 may be openonly adjacent its lower end to receive liquid from one of the lowerzones and adjacent its upper end to discharge liquid conveyed by themember. Alternatively, the member may be open at a plurality oflocations as well as for a substantial portion of its length.

Accordingly, it is to be understood that the drawings and descriptionherein be offered by way of example to facilitate comprehension of theinvention and should not be construed to limit the scope thereof.

What is claimed is:
 1. A thickener/clarifier, comprising: (a) a vesselhaving an inlet for receiving a slurry of a liquid and solid particlessuspended in the liquid, said vessel having an upper portion holding afree settling zone having a relatively low concentration of solid slurryparticles and having a lower portion holding a compaction zone having arelatively high concentration of solid slurry particles and a hinderedsettling zone between said compaction zone and said free settling zone,with said compaction zone and said hindered settling zone constitutinglower settling zones; (b) an overflow launder adjacent said upper end ofsaid vessel for discharge of an overflow phase of the slurry that hasbeen separated in said vessel; (c) an underflow discharge port adjacentsaid bottom of said vessel for discharge of a thickened, underflow phaseof the slurry that has been separated in said vessel; (d) a deliquifyingmember in said vessel extending up from said lower portion of saidvessel to said upper portion of said vessel for flow of free liquidreleased from at least one of said lower settling zones to said freesettling zone while isolating said flow of liquid from the flow ofslurry down in said lower settling zones; and (e) a rake assemblymounted for rotation in said lower portion of said vessel, with saidrake assembly having at least one elongated generally vertical picketforming channels in the slurry held in said lower portion of said vesselfor releasing liquid in at least one of said lower settling zones toflow to said deliquifying member and on to said free settling zone. 2.The thickener/clarifier of claim 1 wherein said rake assembly furtherincludes a rotary drive for rotation of said rake assembly about agenerally vertical axis.
 3. The thickener/clarifier of claim 2 whereinsaid rotary drive is disposed at the upper end of said vessel, saidrotary drive being connected to said rake assembly via an elongate drivemember extending vertically down into said vessel.
 4. Thethickener/clarifier of claim 3 wherein said drive member is of tubularconfiguration for at least a portion of its length to receive liquidreleased from a lower settling zone.
 5. The thickener/clarifier of claim3 wherein said drive member is received in a tubular member surroundingsaid shaft, said tubular member receiving liquid released from a lowersettling zone.
 6. The thickener/clarifier of claim 1 wherein said rakeassembly includes a plurality of pickets extending generally parallel toone another.
 7. The thickener/clarifier of claim 6 wherein said picketsextend into the compaction zone.
 8. The thickener/clarifier of claim 7wherein said deliquifying member is open adjacent its lower end toreceive liquid from at least one of said lower settling zones and saidat least one of said picket extends below said opening adjacent a lowerend of said deliquifying member.
 9. The thickener/clarifier of claim 7wherein said at least of said picket is positioned with its upper endbelow a lower end of said deliquifying member.
 10. Thethickener/clarifier of claim 7 wherein said pickets extend into bothsaid compaction zone and said hindered settling zone.
 11. Thethickener/clarifier of claim 1 wherein said deliquifying member is openadjacent its lower end to receive liquid from at least one of said lowersettling zones and is open adjacent its upper end to discharge liquidconveyed by said deliquifying member to said free settling zone.
 12. Thethickener/clarifier of claim 11 wherein said deliquifying member is opento receive liquid for a substantial portion of its length.
 13. Thethickener/clarifier of claim 11 wherein said deliquifying member is atube with fluid flow openings therein.
 14. The thickener/clarifier ofclaim 13 wherein said deliquifying member has openings at spacedlocations along its length.
 15. The thickener/clarifier of claim 14wherein said deliquifying member has inclined members extending oversaid openings in said deliquifying member in said lower portion of saidvessel.
 16. The thickener/clarifier of claim 11 wherein saiddeliquifying member further comprises an inclined member extending overthe opening in said deliquifying member adjacent its lower end.
 17. Thethickener/clarifier of claim 16 wherein said inclined member comprises aconical baffle.
 18. A method of operating a thickener/clarifier havingan upper portion and a lower portion comprising; (a) feeding a slurry ofa liquid and solid particles suspended in the liquid into a vessel; (b)separating said slurry by gravity into different zones having respectivedegrees of liquid-solids separation including, at a upper portion ofsaid vessel, a free settling zone having a relatively low concentrationof solid slurry particles and further including, at a lower portion ofsaid vessel, a compaction zone having a relatively high concentration ofsolid slurry particles and a hindered settling zone between said freesettling zone and said compaction zone, with said hindered zone and saidcompaction zone constituting lower settling zones; (c) discharging anoverflow phase of the slurry that has been separated in said vessel intoan overflow launder adjacent to an upper end of said vessel; (d)discharging, via an underflow discharge adjacent a bottom of saidvessel, a thickened, underflow phase of the slurry that has beenseparated in said vessel; (e) directing free liquid released from atleast one of said lower settling zones to flow up to said free settlingzone via a flow path isolated from the flow of the slurry down in saidvessel in said lower settling zones; and (f) forming generally upwardlyextending channels in the slurry held in said lower portion of saidvessel to release liquid in at least one of said lower settling zones toflow to said isolated flow path and then on to said free settling zone.19. The method of claim 18 further comprising moving a rake assembly insaid lower portion of said vessel.
 20. The method of claim 19 whereinsaid rake assembly is rotated about a generally vertical axis.
 21. Athickener/clarifier, comprising: (a) a vessel having an inlet forreceiving a slurry of a liquid and solid particles suspended in theliquid, said vessel having an upper portion surrounding a free settlingzone having a relatively low concentration of solid slurry particles andhaving a lower portion surrounding a compaction zone having a relativelyhigh concentration of solid slurry particles, and a hindered settlingzone between said compaction zone and said free settling zone, with saidcompaction zone and said hindered settling zone constituting lowersettling zones and having means for releasing liquid from at least oneof said lower settling zones; (b) an overflow launder adjacent saidupper end of said vessel for discharge of an overflow phase of theslurry that has been separated in said vessel; (c) an underflowdischarge port adjacent said bottom of the vessel for discharge of athickened, underflow phase of the slurry that has been separated in saidvessel; (d) a deliquifying member in said vessel extending up from saidlower portion of said vessel to said upper portion of said vessel forflow of free liquid to said free settling zone released from at leastone of said lower settling zones while isolating said flow of liquidfrom the flow of slurry down in said lower settling zones; and (e) aninjector for injecting flocculant into the flow of water to said freesettling zone to facilitate settling of solid particles in the water.22. The thickener/clarifier of claim 21 wherein the injector extendsinto said deliquifying member.
 23. The thickener/clarifier of claim 21wherein said deliquifying member includes an opening adjacent its upperend for discharge of liquid into said free settling zone and saidinjector is positioned adjacent said opening in said deliquifyingmember.